Bug 2550657 (CVE-2026-79608)

Summary: CVE-2026-79608 xen: xen: Information disclosure via inverted conditional in Zenbleed workaround
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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A flaw was found in Xen. Due to an inverted conditional check in the handling of processor configuration registers, the software mitigation for the Zenbleed hardware vulnerability is not applied when required. A malicious guest user can exploit this lack of protection to access sensitive data belonging to other virtual machines or the hypervisor, leading to information disclosure.
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Bug Depends On: 2559179    
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Description OSIDB Bzimport 2026-10-13 15:54:29 UTC 
The workaround for XSA-433 (Zenbleed, CVE-2023-20593) was later
re-worked to better integrate with other manipulations of the same MSR.
In this rework an inverted conditional was introduced, resulting in the
workaround to not be applied when needed and vice versa.

For more details, see:
  http://xenbits.xen.org/xsa/advisory-433.html